Keyword Research and Adsense
 

It goes without saying, Adsense can be one of the most lucrative ways of making money online. If you have sites generating significant amounts of traffic, you can earn a decent income online with Google’s contextual advertising program. I mean really, when you think about it, what is easier then simply placing a small bit of javascript on the page and earning revenue everytime someone clicks on an ad? Best of all, for the most part, the advertisements displayed are very relevant to the content on the page, so it doesn’t have to be too bold to the visitor.

I agree the keyword research is important. But it's also really important to not try to outsmart the Google engine. Post good honest content and don't go out and put up a spammy set of articles on a subject that have been indexed 18,000 times. Become an expert on something and write your own stuff. The engine will reward this.